Double nut for the controlled tightening of a part by means of a screw connection

ABSTRACT

A double nut for a controlled fixing of a component using a bolt connection, comprising a pulling sleeve having an internal thread adapted to be screwed onto a threaded end of a bolt, and a pressing sleeve adapted to be supported on the component. An internal thread of the pressing sleeve is adapted to be screwed onto an external thread of the pulling sleeve, and engages such external thread to such an extent that the internal thread of the pressing sleeve is spaced by a distance equaling several threads from that end of the pulling sleeve that faces the component. The external thread of the pulling sleeve is furthermore adapted to threadedly receive a pull bushing of a bolt-tightening cylinder that has a support bushing adapted to be supported on the component and to extend over the pulling sleeve and the pressing sleeve.

The invention concerns a double nut for the controlled fixing(tightening or securing) of a part or component by means of a boltedconnection. The double nut comprises a pulling sleeve with an internalthread, which can be screwed onto the threaded end of the bolt, and withan external thread onto which a pressing sleeve, which is supported onthe part or component that is to be fixed by means of the boltconnection, can be screwed. The external thread of the pulling sleevealso serves to screw on a pull bushing of a hydraulic bolt-tighteningcylinder, which comprises a support bushing that engages over thepulling sleeve and the pressing sleeve and is also supported on thecomponent that is to be fixed by means of the bolted connection.

A double nut of the aforementioned kind and a hydraulic bolt-tighteningcylinder that serves for tightening or fixation are described in U.S.Pat. No. 4,844,418 A. The pulling sleeve comprises an external threadthat extends over the entire length of the pulling sleeve. By means ofits internal thread, the pressing sleeve is screwed onto the externalthread of the pulling sleeve. Likewise, the internal thread of thepressing sleeve extends over the entire length of that sleeve, and acollar or flange integrally formed with the pressing sleeve reachesunderneath the pulling sleeve.

In order to tighten the bolt connection, the pull bushing of a hydraulicbolt-tightening cylinder is screwed onto the free end of the pullingsleeve and the bolt-tightening cylinder is pressurized. The supportbushing is supported on a support surface of the component that is to befixed and expands or stretches the bolt so that the pressing sleeve islifted upwardly and away from the support surface. Subsequently, thepressing sleeve can be screwed down towards the support surface, and thecollar on the pressing sleeve moves away from the corresponding end ofthe pulling sleeve. When the pressure in the bolt-tightening cylinder isrelieved, the tension in the bolt is conveyed through the pullingsleeve, the pressing sleeve and the collar on the pressing sleeve to thesupport surface of the component that is to be fixed, so that theinitial tension in the bolted connection is retained.

In the known embodiment of the double nut the stress on the lowerthreads of the pulling sleeve is significantly higher than the stress onthose threads that are in the area where the thread of the pressingsleeve ends. That limits the initial tension that can be applied to thebolt connection, especially if, due to space reasons, the walls of thepulling sleeve and the pressing sleeve have to be kept thin compared tothe diameter of the bolt.

It is therefore an object of the invention to configure the double nutin such a way that the distribution of stress on the threads between thepulling sleeve and the pressing sleeve is as uniform as possible inorder to achieve as efficient a utilization of material as possiblewhile the walls of the pulling sleeve and the pressing sleeve are thin.

Proceeding from that object it is proposed for a double nut of theaforementioned kind that the internal thread of the pressing sleeveengages the external thread of the pulling sleeve at a distance of atleast one thread from that end of the pulling sleeve that is adjacent tothe component that is to be fixed.

Tests have shown that this simple measure results in a significantlyimproved distribution of stress on the threads, so that even if space islimited and the walls of the pulling sleeve and the pressing sleeve arehence thin compared to the diameter of the bolt, a high initial tensioncan be applied and sustained by the double nut.

In order to achieve that the internal thread of the pressing sleeveengages into the external thread of the pulling sleeve at theaforementioned distance of several threads from the end of the pullingsleeve adjacent to the component that is to be fixed, the pulling sleeveand/or the pressing sleeve can be faced or recessed in the area havingno mutual engagement of their threads.

According to a further embodiment, this can also be accomplished byplacing a washer under the pressing sleeve, whereby the washer extendsabout the pulling sleeve and only the pressing sleeve is supported onit.

In that case, the height of the washer should be at least equal to thearea without mutual engagement of the threads of the pulling sleeve andof the pressing sleeve, but it can also exceed that height.

In the area of the washer, the pulling sleeve can be configured withoutan external thread.

In order to be able to apply a sufficiently high initial tension to thebolt connection, even if the parts or components that are to be fixedare of low strength, the washer can have a larger diameter than does thepressing sleeve.

The washer can comprise a countersinking having a cylindrical innersurface that tightly extends around a cylindrical outer surface of thepressing sleeve so as to largely avoid an expanding or breaking of thepressing sleeve under pressure.

In addition to that, the washer can be formed of a high-strengthmaterial, especially if of its height corresponds only to a low numberof threads.

To facilitate the mounting, the washer can magnetically stick to thepressing sleeve, which can e.g. be realized by embedding small permanentmagnets into the washer or by the entire washer being permanentlymagnetic.

The invention is explained in greater detail below with the aid of anembodiment shown in the drawings, in which:

FIG. 1 shows a sectioned view of a double nut according to the inventionwith a washer,

FIG. 2 shows a sectioned view of a double nut according to the inventionwithout a washer, and

FIG. 3 shows a partially sectioned representation of the double orpulling nut according to FIG. 1 with a hydraulic bolt-tighteningcylinder placed.

A part or component 1 that is to be fixed is represented only partiallywith a contact surface 13 for a pressing sleeve 7 and a bore 12 for ascrew-on bolt 2.

The bolt 2 has a threaded end 3 onto which a pulling sleeve 4 is screwedby means of its internal thread 5. The pulling sleeve 4 has an externalthread 6 onto which a pressing sleeve 7, which comprises a cylindricalouter surface 16, is screwed by means of a corresponding internal thread8. A part of the external thread 6 is exposed and serves to screw on apull bushing 24 of a hydraulic bolt-tightening cylinder 18, as it isexplained below with regard to FIG. 2.

The pressing sleeve 7 is supported against a washer 11, resting in acylindrical countersinking having an inner surface 17 of the washer 11.The washer 11 is supported on the contact surface 13 of the component 1that is to be fixed. The cylindrical inner surface 17 of the washer 11tightly embraces the cylindrical outer surface 16 of the pressing sleeve7, so that, in that area, an expanding or breaking of the pressingsleeve 7 under pressure is largely avoided.

As a result of the washer 11, an area of the external thread 6 of thepulling sleeve 4 is not in engagement with the internal thread 8 of thepressing sleeve 7, so that the pulling sleeve 4 has a segment 9 that isnot in engagement with the thread of the pressing sleeve 7.

The height of the segment 9 should equal at least one thread turn orthread and is e.g. determined by the height of the washer 11. Thesegment 9 on the pulling sleeve 4 can be configured without a thread, inother words, faced or recessed.

The same effect can be achieved if no washer is used, as represented inFIG. 2; rather, the pressing sleeve 7 is directly supported on thecontact surface 13 and at least the internal thread 8 of the pressingsleeve 7 or the external thread 6 of the pulling sleeve 4 or both arecorrespondingly faced or recessed.

The height of the section 9, which is determined either by the washer 11or by the aforementioned facing, is insignificant. It has to measure atleast one course of thread, but can also be considerably higher becausethe relieving effect for the first thread of the pulling sleeve 4 occursin any case and the stress is distributed over a greater number ofthreads as in the embodiment according to the U.S. Pat. No. 4,844,418 A.

As represented, the diameter of the washer 11 can be greater than theouter diameter of the pressing sleeve 7 and can, with a small free spaceor play, be equivalent to the diameter of a countersinking 15. In thatcase, as described below, a support bushing 20 of the hydraulicbolt-tightening cylinder 18 is supported on the surface of the washer11. If the outer diameter of the washer 11 is equal to the outerdiameter of the pressing sleeve 7, which is also possible, the supportbushing 20 is supported directly on the contact surface 13.

Small permanent magnets 14 are embedded in the washer 11 and facilitatemounting since the washer 11 then adheres or sticks to the pressingsleeve 7.

The same effect is achieved if the entire washer 11 is permanentlymagnetic.

Preferably, the washer 11 is formed of a high-strength material so thata high initial tension in the boltconnection can be realized even on acomponent made of lesser strength material.

FIG. 3 illustrates how the bolt 2 is tightened. First, the pullingsleeve 4, having the pressing sleeve 7 with the adhering washer 11already screwed onto it, is screwed onto the threaded end 3 of the bolt2 until the washer 11 rests against the component 1 that is to be fixed.Subsequently, a pull bushing 24 having an internal thread is screwedonto the part of the external thread 6 of the pulling sleeve 4 that isstill exposed. The pull bushing 24 is part of a hydraulicbolt-tightening cylinder 18 and is screwed on until an area of thesupport bushing 20 which extends around the pressing sleeve 7 issupported on the washer 11. Simultaneously, an inner toothing (notrepresented in detail) on a rotation bushing 21 is brought intoengagement with a corresponding outer toothing 10 or the like on thepressing sleeve 7. When hydraulic liquid under pressure is supplied tothe hydraulic bolt-tightening cylinder 18 via a pressure connection 19,the pull bushing 24 pulls the pulling sleeve 4 upwardly while thesupport bushing 20 is supported on the washer 11. In that way, the boltis expanded or stretched to the prescribed extent, which can e.g. bedetermined directly my means of a marking on the pulling sleeve. At thesame time, the pressing sleeve 7 is lifted upwardly and away from thecomponent 1 that is to be fixed and can easily be screwed down, by meansof a rotating drive 22, until it rests against the washer 11. When thepressure in the hydraulic bolt-tightening cylinder 18 is thereafterrelieved, the expansion of the bolt 2 is retained and the hydraulicbolt-tightening cylinder 18 can be screwed off the pulling sleeve 4 andused for a further tightening procedure.

If the hydraulic bolt-tightening cylinder 18 does not comprise arotational drive 22, the pressing sleeve 7 can be screwed down byintroducing a pin through an opening 23 and inserting it into bores (notrepresented) in the pressing sleeve 7. The pressing sleeve 7 can then bescrewed down with the aid of the pin.

A suitable hydraulic bolt-tightening cylinder for tightening the doubleor pulling nut comprising the pulling sleeve 4 and the pressing sleeve 7is described in commonly owned DE 196 38 901 A1.

1-10. (canceled)
 11. A double nut for a controlled fixing of a componentby means of a bolt connection, comprising: a pulling sleeve having aninternal thread, which is adapted to be screwed onto a threaded end of abolt, and also having an external thread; and a pressing sleeve that isadapted to be supported on said component, wherein said pressing sleevehas an internal thread via which said pressing sleeve is adapted to bescrewed onto said external thread of said pulling sleeve, wherein saidinternal thread of said pressing sleeve engages said external thread ofsaid pulling sleeve to such an extent that said internal thread of saidpressing sleeve is spaced by a distance equaling several threads from anend of said pulling sleeve that faces said component, and wherein saidexternal thread of said pulling sleeve is furthermore adapted tothreadedly receive a pull bushing of a hydraulic or pneumaticbolt-tightening cylinder that is also provided with a support bushingthat is adapted to be supported on said component and to extend oversaid pulling sleeve and said pressing sleeve.
 12. A double nut accordingto claim 11, wherein at least one of said pulling sleeve and saidpressing sleeve are faced or recessed in an area in which said externalthread of said pulling sleeve and said internal thread of said pressingsleeve do not inter-engage.
 13. A double nut according to claim 11,wherein a washer is provided that extends about said pulling sleeve andwherein said pressing sleeve is supported on said washer.
 14. A doublenut according to claim 13, wherein said washer has a height thatcorresponds to an area in which said external thread of said pullingsleeve and said internal thread of said pressing sleeve do notinter-engage.
 15. A double nut according to claim 13, wherein saidwasher magnetically sticks to said pressing sleeve.
 16. A double nutaccording to claim 15, wherein small permanent magnets are embedded insaid washer.
 17. A double nut according to claim 15, wherein said washeris permanently magnetic.
 18. A double nut according to claim 13, whereinsaid washer has a diameter that is greater than a diameter of saidpressing sleeve.
 19. A double nut according to claim 13, wherein saidwasher is provided with a countersinking having a cylindrical innersurface that extends tightly about a cylindrical outer surface of saidpressing sleeve.
 20. A double nut according to claim 13, wherein saidwasher is made of a high-strength material.